Field of the Invention
The present invention relates generally to an alarm for detecting the unauthorized opening of a door, and more particularly to an improved lightweight, portable, wireless electronic alarm device which may be easily installed as a wedge at the base of an inwardly-opening door to resist forced opening of the door while simultaneously sounding a highly audible alarm signal indicative of an attempt to break in.
One of the consequences of our increasingly crowded urban society has been the inexorably increasing crime rate, the mere threat of which has driven many people to be security-conscious. Breaking and entering and burglary have become increasingly common occurrences, particularly in the case of residential property. Accordingly, the sale and installation of various security systems such as burglar alarms has become a thriving business as many property owners seek to discourage crime to property through the use of such systems.
There are two basic types of security systems: first, the professionally-installed central security system, which is used in privately-owned houses and luxury apartments, and secondly the owner-installable or portable systems of various types which are each installed, for example, on a single door. The second type of device is particularly used by apartment dwellers, both since the purchase of such systems is more economical, and since they can usually be removed and taken when the owner of the device moves. They also find substantial use in homes of people who do not wish to pay the high price of a central security system.
In most apartments and homes the doors are side-hinged inwardly-opening doors, which open by pulling the opening edge of the door inward and which close by pushing the opening edge of the door outward. A number of the relatively inexpensive, owner-installable security devices have been designed for use with such inwardly-opening hinged doors. Typical of one type of such systems are those shown in U.S. Pat. No. 2,870,281, to Mitchell, in U.S. Pat. No. 4,442,427, to Morton, and in U.S. Pat. No. 4,607,253, to Wooten, et al. These devices act as braces installed with one end under the doorknob and the other end on the floor away from the door. When the door is opened slightly, these devices will inhibit the door from opening and will provide an audible alarm.
Such devices function admirably, but they are relatively large and bulky, since they need to reach from the doorknob to the floor at an angle. Thus, they require an area for storage since they can not just be placed on a table or desk or in a bookcase. In addition, they are not desirable to travelers due to their inconvenient size. Finally, they are an eyesore when installed on a door, typically extending out into the room at an angle from the door.
The other type of device is illustrated by U.S. Pat. No. 4,540,980, to Porco. The Porco device is illustrative of those devices which are placed in front of an inwardly-opening hinged door. When the door is opened, the device will be jarred or tipped over, causing an alarm to be sounded. Other similar devices are designed to be hung from the doorknob, and will react to the door being opened through the use of motion detectors.
This type of device is advantageous in that it is typically small and portable, and is frequently used by travelers. However, unlike the first type of device, the second type of device does not prevent a door from being opened. Rather, it will just alert the user that someone has opened the door. It is thus a warning type device rather than a security-enhancing type of device.
It is accordingly the primary objective of the present invention that it provide a design for an alarm which will fit any hinged inwardly-opening door. It is an objective that the device of the present invention sound an alarm when the door is opened a very small amount, that full opening of the door not be necessary in order to set off the alarm. It is another primary objective that, as the device begins to sound an alarm indicating attempted forced entry, it also blocks further opening of the door to prevent access through the door. The device of the present invention should thus effectively prevent the door from being opened from the outside.
The alarm device of the present invention should work with any hinged, inwardly-opening door. It is also an objective of the alarm device of the present invention that it be both simple and easy to install. No tools may be required in the installation, and installing the device should not result in any damage to the door on which the device is installed. It is a particular disadvantage of highly visible devices that they are not aesthetically pleasing. As a result, highly visible devices will not be desirable to a large number of prospective buyers even though the visibility may have some effect to discourage intruders. Therefore, the alarm device of the present invention should be unobtrusive when installed so as not to effect a disconcerting presence inside the property.
It is also apparent to those skilled in the art that by making the alarm device of the present invention portable as well as easy to install without requiring tools. In addition, of course, it is desirable that the improved alarm device of the present invention be mechanically simple to ensure reliable operation. Therefore, as few moving parts as possible should be utilized, to enhance the reliability of the device. The operation of the device should sound an alarm when a forced entry is attempted.
In addition, the improved alarm device of the present invention should also be of solid state construction, to ensure a long, reliable lifetime as well as energy efficient operation. When the alarm is sounded, it should continue until the device is reset, with the resetting operation being simple yet not obvious upon initial inspection. The alarm of the present invention should also be of inexpensive construction, thereby ensuring the broadest possible appeal in the alarm market. Finally, the improved alarm of the present invention should provide all of the aforesaid advantages and objectives without incurring any substantial relative disadvantage.